3- POINT BENDING

Cairo University Faculty Of EngineeringAerospace Engineering Department

Class : 1st Year

Submitted To : Prof. / Mohammed Tawfik

Contents

Defining the Problem Proposed solutions Final design Execution Testing Practical problems

Defining the problem:

Finding a suitable device which is capable of measuring the deflection in any thin beam due to the applied bending moment. To do this we realized we must apply a perpendicular force to the beam while it is held by two supports.

We thought about many solutions

but some of them were impractical and others were too expensive to implement. Some of those thoughts is presented in the following lines.

Proposed solutions:

Trying to build a computerized model

Its idea was to apply the force by using hydraulic press and measure it by using an electronic sensor connected to a computer. In addition of measuring the deflection in the beam by an electronic micrometer also connected to the computer. Then graphing the relation between the applied moment and deflection, but we found it very complicated and needs more experience.

We tried to simplify our concept and achieve a simple design by fixing the supports in the base and applying the load by attaching it to a movable hook sliding on the rod. Further more, measuring the deflection using spring micrometer. But we found that in this design we cant measure the deflection in the point which we apply the load on. Moreover, the tips of the supports were u-shaped so, the reaction acts on a circular surface not in a certain point.

Simple Design

We improved our design to over come those problems by using a knife -edge tips and changing the way we apply the load as shown in figure

Final design

Testing

We have used this device to make different experiments:

Applying fixed load at the center of the rod and measuring the deflection at different points.

Applying fixed load at different positions and measuring the deflection.

Measuring the modulus of elasticity of an unknown material.

0 5 10 15 20 25 30

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0

Position of measuring point

Applying fixed load on the center of aluminum rod

Defl

ecti

on i

n m

m

0 5 10 15 20 25 30

-1.2

-1

-0.8

-0.6

-0.4

-0.2

0

Applying fixed load in different positions on yellow cupper rod Position of measuring point

Defl

ecti

on

in

mm

0 5 10 15 20 25

-0.3

-0.25

-0.2

-0.15

-0.1

-0.05

0

Measuring point position

Deflecti

on i

n m

mApplying fixed load in n0n – Centric positions on

yellow cupper rod

0 2 4 6 8 10 12 14 16 18 20

-0.25

-0.2

-0.15

-0.1

-0.05

0

Measuring point position

Deflecti

on i

n m

m

Y

X

P

L/2 L/2

Used Relations

Practical Problems o Adjusting the orientation of the cylindrical

supports’ knife perpendicular to the edge of the rod .

o The tips of the cylindrical supports weren’t accurate enough .

o The cylindrical supports slide hardly in the slot .

Prepared by :Abdelrahman Hussien MahmoudAhmed Fathy El-ShazlyAhmed Fawzy El-Araby Ahmed M. Zaki Alaa Mohammed AbdullahAmr Mahmoud Lotfy Cindrella Mohamed OkashaRadwa Magdy Abdelmohsen Marco Mounir Abdallah Mohamed Samy El-Alfy

THANK YOU

Questions ?